Active energy ray curable compositions have been hitherto supplied and used for offset printing, silk screen processing, overcoat agents and the like. In recent years, the amount of use of the active energy ray curable compositions is ever increasing due to the advantages such as cost reduction as a result of simplification of the drying process, and reduction of the volatilization volume of the solvent in coping with environmental problems. Among others, water-based compositions and solvent-based compositions are extensively used as inkjet inks, and these compositions can be used appropriately for different applications in accordance with the characteristics of the respective compositions. However, these water-based and solvent-based compositions have problems such as limitations on the receptor base material in industrial use, relatively poor water resistance, a need for a large amount of energy for the drying of the ink, and adhesion of the ink components to the head as a result of drying. Therefore, it is expected that the ink compositions be replaced with active energy ray curable inks having relatively low volatility.
Active energy ray curable inks are expected to be able to cope with various base materials. However, in reality, the extent of dot spread of the ink varies according to the difference between the surface tension of the base material and the surface tension of the ink, so that it is difficult to obtain satisfactory image quality equally with all base materials. Particularly, absorbing media such as paper are prone to have vertical penetration, and dot spread does not easily occur in the absorbing media as compared with non-absorbing media.
Patent Document 1 discloses that printing is performed using a UV ink by an inkjet method on a coated paper, but a cationic type inkjet ink is used. Furthermore, this technology suggests a gesture of suppressing dot spread, so that it is difficult to obtain satisfactory image quality when images are printed.
Patent Document 2 discloses the use of dipropylene glycol which exhibits satisfactory spread on coated paper. However, a hydrogen-withdrawing type initiator is not used, and highlighted parts are not cured.
Patent Document 3 discloses the use of dipropylene glycol and a hydrogen-withdrawing type initiator. However, the amount of dipropylene glycol is small, and sufficient spread does not occur in coated paper. Furthermore, benzophenone is used as the hydrogen-withdrawing type initiator, but benzophenone has strong light absorption in the shorter wavelength region and is likely to cause curing defects such as surface wrinkles.
Patent Document 4 discloses the use of 1,9-nonanediol diacrylate which exhibits satisfactory spread on coated paper. However, as in the case of Patent Document 3, benzophenone is used as a hydrogen-withdrawing type initiator, and curing defects are prone to occur.
Patent Document 1: Japanese Patent Application Laid-Open (JP-A) No. 2005-144790
Patent Document 2: JP-A No. 2007-262218
Patent Document 3: JP-A No. 2008-189887
Patent Document 4: JP-A No. 2007-231232